Release 7 of the third generation partnership program (3GPP) TR 25.903 V7.0.0 (2007-03) technical report defines a capability for packet data users called Continuously Packet Connected or Continuous Packet Connectivity (CPC). A mobile user equipment (UE), such as a cell phone, that has both a CPC capability and a low data rate requirement may selectively switch off some UE circuits to save battery power. For example, a UE that transfers voice over internet protocol (VoIP) data packets to and from a cellular base station (BS) or cell of a cellular network can switch on the radio frequency (RF) front end and other selected circuits, process voice data packets, then switch off the RF front end and other selected circuits.
A UE that switches receiver and transmitter circuits on and off as needed uses the discontinuous reception (DRX) and discontinuous transmission (DTX) features of CPC. The DRX and DTX features can save battery power and extend the connect or talk time of the UE. For example, a UE that receives a 2 ms data packet in a transmission time interval (TTI) every 20 ms can use the DRX feature to reduce the average power to the RF and selected circuits by 90%.
The DRX feature can interact with mobility measurements that determine which cells the UE can or might communicate with. The mobility measurements are performed by the UE and can include: 1) identifying cells, 2) measuring and reporting the identified cells to the cellular network, and 3) receiving a command from the network to add a newly identified cell to the set of active cells. Active cells are BSs that can transfer packets to or receive packets from the UE. One of the active cells may be designated as the serving cell.
Mobility measurements are reported to the network in accordance with cellular telephony standards, such as the 3GPP TS 25.133-7.8.0 technical specification. For example, section 8.1.2.2.2 (“UE CPICH measurement capability”) of TS 25.133-7.8.0 specifies the rate at which cells should be measured and how fast a newly identified cell should be reported to the network. Specifically, TS 25.133-7.8.0 requires 1) identifying a newly detectable cell within 800 ms and 2) reporting eight identified cells every 200 ms. In general, the process of identifying a new cell is longer and more power-consuming than measuring an already-identified cell, whereas a mobility measurement on a previously identified cell may consume very little UE power in comparison.
One proposed modification to TR 25.903 V7.0.0 (2007-03) calls for making the mobility measurement interval proportional to the percentage of a DRX cycle that the UE receiver is active. For example, a UE that has a 10% activity factor may take 8 seconds to detect a new cell, rather than 800 ms. Such proposed modifications may reduce the mobility of a UE that uses CPC, especially for small activity factors, and may lead to a larger probability of dropped calls. For example, if the time that a UE uses to identify a new cell increases, then there is an increased probability that the cell will become obsolete or unsuitable for data packet transfer due to motion of the UE, the signal propagation condition change, and the like.